The present invention relates in general to devices used for removing heat from electronic modules, and methods of constructing such devices. In particular, the present invention relates to an apparatus for passivating an electronic module substrate assembly by preventing contact between a cooling fluid and the electronics to be cooled while providing a high thermal conductivity path between the electronics to be cooled and the cooling fluid.
As is known, operating electronic devices produce heat. This heat should be removed from the devices in order to maintain device junction temperatures within desirable limits: failure to remove the heat thus produced results in increased device temperatures, potentially leading to thermal runaway conditions. Several trends in the electronics industry have combined to increase the importance of thermal management, including heat removal for electronic devices, including technologies where thermal management has traditionally been less of a concern, such as CMOS. In particular, the need for faster and more densely packed circuits has had a direct impact on the importance of thermal management. First, power dissipation, and therefore heat production, increases as the device operating frequencies increase. Second, increased operating frequencies may be possible at lower device junction temperatures. Finally, as more and more devices are packed onto a single chip, power density (Watts/cm2) increases, resulting in the need to remove more power from a given size chip or module. These trends have combined to create applications where it is no longer desirable to remove the heat from modern devices solely by traditional air cooling methods, such as by using traditional air cooled heat sinks. These trends are likely to continue in the foreseeable future, furthering the need for alternatives to traditional air cooling methods.
One approach to avoiding the limitations of traditional air cooling is to use a cooling fluid. As is known, different fluids provide different cooling capabilities. In particular, fluids such as refrigerants or other dielectric fluids exhibit relatively poor thermal conductivity and specific heat properties, when compared to fluids such as water or other aqueous fluids. Dielectric fluids have an advantage, however, in that they may be placed in direct physical contact with electronic devices and interconnects without adverse affects such as corrosion or electrical short circuits. For example, U.S. Pat. No. 6,052,284, entitled xe2x80x9cPrinted Circuit Board with Electronic Devices Mounted Thereon,xe2x80x9d describes an apparatus in which a dielectric fluid flows over and around several operating electronic devices, thereby removing heat from the devices.
Other cooling fluids, such as water or other aqueous fluids, exhibit superior thermal conductivity and specific heat compared to dielectric fluids. Water-based coolants, however, must be kept from physical contact with electronic devices and interconnects, since corrosion and electrical short circuit problems are likely to result from such contact. Various methods have been disclosed for using water-based coolants, while providing physical separation between the coolant and the electronic devices. For example, U.S. Pat. No. 4,531,146, entitled xe2x80x9cApparatus for Cooling High-Density Integrated Circuit Packages,xe2x80x9d discloses the use of a conductive foil barrier; U.S. Pat. No. 4,879,629, entitled xe2x80x9cLiquid Cooled Multi-chip Integrated Circuit Module Incorporating a Seamless Compliant Member for Leakproof Operation,xe2x80x9d and IBM Technical Disclosure Bulletin Vol. 20, No. 2, July 1977, entitled xe2x80x9cLiquid Cooled Module with Compliant Membrane,xe2x80x9d disclose the use of a flexible barrier with thermal conduction enhancements (thermal studs and heatsinks, respectively); and U.S. Pat. No. 4,381,032, entitled xe2x80x9cApparatus for Cooling High-Density Integrated Circuit Packages,xe2x80x9d and U.S. Pat. No. 5,294,830, entitled xe2x80x9cApparatus for Indirect Impingement Cooling of Integrated Circuit Chips,xe2x80x9d disclose the use of flexible barriers, where pistons are used to maintain contact between the barrier and the devices to be cooled.
An additional problem may arise with the use of a barrier, where the barrier material differs from any of the other materials used to construct the electronic module assembly. While solids in general tend to expand with increasing temperature, the rate of expansion for a given temperature change tends to be characteristic of a particular material. This characteristic, known as the thermal coefficient of expansion, varies from material to material. Therefore, two structures of different materials, when bonded together at one temperature, will tend to expand at different rates as the temperature of the two materials increases. This difference in expansion rates results in mechanical stresses in the structure, as the temperature of the structure varies in either direction from the temperature at which the devices were bonded (zero stress condition). It is desirable, therefore, for a device employing a coiling fluid barrier to provide a stress relief mechanism in order to relieve stresses produced within permanently bonded structures composed of materials having different thermal coefficients of expansion.
For the foregoing reasons, therefore, there is a need in the art for a device capable of providing a high thermal conductivity path between a device to be cooled and a water-based coolant, while simultaneously maintaining physical separation between the coolant and electronic devices and providing relief from mechanical stresses caused by mismatches in the thermal coefficients of expansion of various materials within the device assembly.
The present invention is directed to a device capable of providing a high thermal conductivity path between a device to be cooled and a water-based coolant, while simultaneously maintaining physical separation between the coolant and electronic devices and providing relief from mechanical stresses caused by mismatches in the thermal coefficients of expansion of various materials within the device assembly.
In one aspect of the present invention, an electronic module substrate assembly is disclosed, including a substrate, an electronic device which is electrically connected to the substrate, and a metal barrier. The substrate includes a periphery. The metal barrier includes a perimeter area which is sealably affixed to the substrate periphery; at least one fold to accommodate thermal expansion; and a device contact area which is thermally coupled to an upper surface of the electronic device.
In another aspect of the present invention, an electronic module assembly is disclosed, including a substrate, an electronic device which is electrically connected to the substrate, and a metal barrier. The substrate includes a periphery. The metal barrier includes a perimeter area which is sealably affixed to the substrate periphery; at least one fold to accommodate thermal expansion; and a device contact area which is thermally coupled to an upper surface of the electronic device. The electronic module assembly further includes a module cap sealably affixed to the upper surface of the barrier perimeter area, the module cap inner surface and the barrier upper surface thereby defining an internal volume capable of containing a cooling fluid.
In yet another aspect of the present invention, a method of fabricating a passivated electronic module substrate assembly is disclosed. The substrate assembly includes a substrate and at least one electronic device. The substrate includes a perimeter area. The method includes: sealably affixing a metal barrier to the substrate perimeter area, where the metal barrier includes at least one fold to accommodate thermal expansion; thermally coupling the metal barrier to at least one electronic device.
It is therefore an object of the present invention to provide a passivated electronic module substrate assembly. It is a further object of the present invention to passivate an electronic module assembly by providing a thermally conductive barrier, thermally coupled to at least one electronic device. It is a further object of the present invention to provide relief from mechanical stresses caused by mismatches in thermal coefficients of expansion by using a folded barrier.
The recitation herein of a list of desirable objects which are met by various embodiments of the present invention is not meant to imply or suggest that any or all of these objects are present as essential features, either individually or collectively, in the most general embodiment of the present invention or in any of its more specific embodiments.